The invention relates to a method for grinding bar-shaped workpieces, which have a non-circular cross-section formed by flat and/or curved lines and flat faces extending parallel to each other.
A preferred field of application, which is mentioned, by way of example, for such bar-shaped workpieces, is mechanical adjusting, switching and control devices, in which bar-shaped parts function as actuators and transmit movements and forces. In this case, the bar-shaped workpieces can preferably have lengths between 20 and 80 mm, and a square cross-section preferably having an edge length between 4 and 15 mm. Various metals, as well as ceramics, are possible as materials. The non-circular cross-section means that, with appropriate guidance, the bar-shaped actuators are only displaced in the longitudinal directions thereof and, when mounted, do not twist.
In this application, very high demands are placed on the finished bar-shaped workpiece. In particular, the dimensional accuracy of the basic dimensions, the parallelity of the faces, exact compliance with right angles between the longitudinal sides and faces, the flatness of the faces, and a maximum roughness profile height Rz are noted.
The precision required in practical applications can presently only be achieved by machining each side of the bar-shaped workpiece individually by means of horizontal surface grinding. This method, however, is limited to geometric cross-sections with straight edges. With this grinding method, it is difficult to supply the grinding zone with cooling lubricant, due to the surface contact with the grinding wheel. For this reason, the time savings achieved is not as great as with peripheral grinding. Furthermore, the frequency with which the workpiece must be turned and rechucked prevents economical mass production.
For grinding the faces of pins and similar parts, the double-disk face grinding method is known, for example, using a machine made by the applicant with the model name Saturn H (Junker brochure, partner for precision, of Feb. 6, 2002, FIGS. 86 and 87). To this end, a rotating carrier disk, comprising axially extending bores in the circumferential region thereof, serves as the workpiece holder. The pins are located in the bores and protrude laterally beyond the lateral faces of the carrier disk. Two rotating grinding wheels, which are disposed coaxially at a distance from each other, are positioned on either side of the rotating carrier disk at the periphery thereof, the distance between the grinding wheels corresponding to the grinding dimensions for the pins. In this manner, face-grinding is simultaneously performed on the faces of many pins by the lateral surfaces of the grinding wheels.
This known method cannot easily be applied to the grinding of the bar-shaped workpieces mentioned above. Firstly, the blanks for these workpieces have different grinding allowances. As a result, mounting in simple recesses in a carrier disk is not possible, as non-circular cross-sections are assumed. An imprecise fit in the carrier disk would negatively impact the parallelity of the faces as well as the compliance with exact right angles between the faces and lateral surfaces. Furthermore, grinding in individual lots is not in keeping with the requirements of high-volume production, if not only the faces, but also the flat longitudinal sides, of the bar-shaped workpieces are to be ground in large numbers. There is also a need for configuring the non-circular cross-sections of the bar-shaped parts in a variable manner, so as to include curved lines. The bar-shaped workpiece may even require a longitudinal contour, deviating from the parallel course of two straight lines.
It is therefore the object of the invention to design a method of the type described above, so that economical mass production and excellent grinding results are achieved, and whereby various cross-sectional shapes and longitudinal contours can be ground for the bar-shaped workpieces.